1. Field of the Invention
The present invention relates to glass fibers coated with a sizing composition which is intended to confer on them certain properties, for the purpose of reinforcing organic materials or "organic matrices".
More precisely, the present invention relates to glass fibers which are coated with a suitable sizing composition and are intended for reinforcing thermoplastic matrices such as polyolefin matrices and, more particularly, polypropylene matrices. The present invention also relates to the reinforced products produced.
2. Description of the Background
The capacity of a glass fiber to receive various sizing compositions creating a bond between the glass and the matrix to be reinforced enables the fiber to be associated with numerous polymeric materials in order to produce composite products the properties, particularly mechanical properties, of which are better than those of the non-reinforced polymeric material.
Glass fibers are generally coated with sizing compositions when they are in the form of filaments as they are drawn from the dies, the sizing being intended, in the first place, to ensure bonding between the filaments and to protect the threads produced by the assembly of the filaments against abrasion. At the same time, as indicated above, the sizing promotes adhesion between the glass threads and the materials which they are to reinforce.
In the case of glass fibers which are intended to reinforce thermoplastic matrices such as polyolefin matrices and, particularly, polypropylene matrices, it is known to use sizing compositions based on an emulsion of polyolefins of a nature closely related to that of the polyolefins constituting the matrix to be reinforced. It is also known that the cohesion between the glass fibers and the polyolefin matrices is facilitated by the presence, on the polyolefins of the emulsion, of reactive groups, such as carboxyl groups, which can react with other compounds present in the sizing composition. The presence of grafted polyolefins of this type within the sizing composition is all the more necessary to ensure good glass-matrix bonding as the matrices themselves lack such reactive groups.
In order to improve cohesion between the grafted or non-grafted polyolefin matrices and the glass fibers, it is also known to use, for the reinforcement of the matrices, glass fibers coated with a composition comprising an emulsion of polyolefins onto which acids are grafted, which acids are neutralized by diethylethanolamines, in the presence of at least one aminosilane coupling agent which has a basicity greater than that of the diethylethanolamine and which reacts with the salts of neutralized polyolefins, and also comprising at least one stabilizing agent in the form of a diacid, as well as an adhesive film-forming agent. This composition, which is described in U.S. Pat. No. 5,130,197, generally involves the use of aminosilanes having very reactive amine groups and/or the use of aminosilane in relatively large quantities, this being particularly unfavorable in terms of cost. Moreover, the phenomenon of significant thickening has been noted when the stabilizing agent or the silanes are added over the course of the production of the sizing composition, which thickening may increase with time, or may stabilize, according to circumstances. A need, therefore, continues to exist for a sizing composition which results in improved bonding between glass fibers and polymer matrix.